To execute bending work for making a flange piece the outside without deforming the flange part by connecting a reinforcing piece which is extended from a position except the flange piece extending part of hollow extruded shapes for bending to the flange piece.

The extruded shapes 1 have a hollow cross section and made into an unequal-sided hexagon. A 1st flange piece 3 which is obliquely upward extended from the 1st corner part (flange piece extending part) 2a of the main body 2 of the shapes and the 2nd flange piece 4 which is extended from the 5th corner part 2c and becomes a drip flange are provided. Furthermore, the reinforcing piece 5 which is extended from the 2nd corner part 2b of the main body 2 of the shapes toward the 1st flange piece 3 is provided. This reinforcing piece 5 is connected to the 1st flange piece 3 in the position where is slightly on the side of the base end from the tip part 3a of the 1st flange piece 3. When this shape 1 is bent putting the 1st flange piece 3 on the outside, the 2nd flange piece 4 is abutted on a bending die D and the 1st flange piece 3 is restrained with the reinforcing piece 5, so the shapes are bent without causing any deformation.